Well, I’m just finishing a cutting board for my niece. Bought some nice quarter-sawn white oak and it came out great. That is, until I sanded and then wet the surface to raise the grain. After wiping the surface with a damp rag, I noticed all these dark grain lines in the surface. The second pictures shows it well.

I am unsure if there was a reaction to the water or if the water removed the sanding dust and revealed that the sandpaper left it’s grit behind in the grain lines. I suspect the latter.

I tried to remove it by wetting the surface with alcohol and scrubbing with a clean toothbrush, but that had no effect.

Has anyone had this problem? And if so, what is the fix? I’m probably going to try scraping the surface again to remove it (finally got my #80 to work properly).

Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/

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[Andrew LeslieParticipant @joopson]

I’ve yet to work in any Oak, so take this with a grain of salt; but, could it simply be that this is one of the characteristics of the wood you’ve used? I definitely don’t think it looks bad, whatever the case.

[Joe KaiserParticipant @jotato]

Oak is full of tanin and will react easily with iron and water. I don’t know the chemistry off the top of my head, but it does cause into turn black.

Basically, if you wet the surface and there was any iron dust on the rag, or the wood it will do this. You can use it to your advantage. Soak steel wood in vinegar for a bit. Then apply the “stain” to woods high in tanin. The effect is aged wood.

Just random thoughts while I eat cake. I am not expert.

Seattle, WA

[WesleyParticipant @weslee]

Agree with Joe. Maybe the rag wasn’t clean, maybe your hands weren’t clean after sharpening. The same thing happened to me yesterday in a piece of cherry. In my case I was able to plane it out easily.

Wesley

• This reply was modified 3 years, 5 months ago by Wesley.

[ArchieMember @archie]

First thing’s first, nice job! I would go with a really sharp smoothing plane to take out the stains. And if i remember correctly you should be using food grade mineral oil on the cutting board then sealing it with bees wax.

Good Luck.

[Matt McGraneParticipant @mattmcgrane]

OK, thanks everybody. I knew about the iron effect with oak tannins. I don’t think I used a dirty rag, but it is possible that the rag I dampened to wipe the cutting board was dirty, possibly with metal dust from sharpening. Or maybe it had been contaminated.

I’m doing an experiment today on a piece of scrap. One side was sanded (after planing) and the other side was just finish planed. Then I wiped the whole thing with a damp rag. I just went out to the shop to look at it and the sanded side shows some staining. So my conclusion is that my sandpaper is causing the problem. I use silicon carbide wet-dry paper (only dry) that is dark grey in color. Maybe I need to find some light colored Aluminum oxide paper.

Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/

[Peter GeorgeParticipant @pjgeorge]

That sounds like it may be the problem. I had the same problem when sanding objects on the lathe. The dark silicon carbon paper would leave dark particles embedded in the wood. This was particularly bad with open pored woods, and from the pictures it looks like the same problem I was having.

Since then, I’ve reserved the silicon carbide for lapping metal etc.

Peter in
Biggar SK
"New York is big, but this is Biggar"

[Matt McGraneParticipant @mattmcgrane]

@pjgeorge – so Peter, did you go to Aluminum Oxide paper for sanding wood and lathe work? Or some other type of sand paper?

Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/

[Peter GeorgeParticipant @pjgeorge]

Yes, I use aluminum oxide paper. I really like the Norton 3X or the 3M “No Load”. These have a coating which helps prevent the sand paper from clogging and the backing paper is stronger than the regular hardware store stuff. That’s probably less of an issue with hand sanding.

I mostly only use 220x or finer and a box of 20 sheets lasts a long time.

Peter in
Biggar SK
"New York is big, but this is Biggar"

• This reply was modified 3 years, 5 months ago by Peter George.

[Brett aka PheasantwwParticipant @pheasantww]

Matt, When I get pours that fill up with sanding residue I will “paint” on some mineral oil then wipe it right off and poof the residue disappears. It sounds goofy but it works.

Located in Honeoye Falls NY USA. The Finger Lakes region of Western NY.

"If you give me 6 hours to fell a tree, I will take the first 4 to sharpen my axe" Abe Lincoln

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